1. Field of the Invention
The present invention relates to packaged devices and particularly to packaged devices containing mechanically sensitive components. A mechanically sensitive component or an active region, respectively, is, for example, an SAW or BAW filter or a micromechanical element.
2. Description of the Related Art
Micromechanical devices play an increasingly important role, particularly when considering rotation rate sensors, acceleration sensors, etc. Here, a mechanically active part such as a mass that is deflectable depending on acceleration, or a vibrator that may be put in stimulating vibration in a rotation rate sensor, or generally a sensor or actuator is packaged together with an integrated circuit for controlling and/or evaluating the device. Other elements whose characteristics are affected by a casting package, such as bulk acoustic wave filters (BAW filters) or surface acoustic wave filters (SAW filters), are also packaged either on their own or together with an integrated circuit for controlling or readout.
Typical packaging concepts, such as casting or molding in plastic or resin, are disadvantageous in that the mechanical properties of mechanically sensitive parts may be affected, or, like in the case of BAW or SAW filters, in that the material on the surface of the BAW resonators also has an influence on the characteristics of the filter.
For the protection of mechanical structures, wafers with corresponding structures, i.e. filters, resonators, sensors, or actuators, etc., have been bonded with a second wafer into which pits and holes are etched in the places of the structure, so that the pits of the second wafer form cavities over the sensitive structures of the first wafer and the holes in the second wafer (cap wafer) make contact pads of the first wafer accessible. Thereby the sensitive structures are protected. Alternatively, ceramic packages also are employed, which are, however, expensive.